|You can use a Y cable - a Y splitter cable - a cable with a 15 pin male connector to two 15 pin female connectors - to connect two monitors to one video port, but often the video is not as good on both monitors as it was on one.|
You can buy video splitter (hardware) boxes - they amplify the signal so each monitor has a strong enough signal - that's what is used in stores to display the same thing on many computer monitors.
Ones to connect to two or a few more VGA monitors are relatively cheap. You also need a short video extension cable (15 pin VGA, usually male to female, depending on the input port on the box).
The video on the two monitors is identical of course, and you will not see two displays for monitors in the Display properties in Windows because Windows
isn't aware there are two monitors connected to the same port. In some cases you see two displays in the Display properties but the other one is for TV Out video - SVideo or composite video..
If you want the possibility of the displays being different or having different settings for each monitor, you need to install a video card with two or more monitor ports. Ones with two video ports are common.
However, when you do use a video card that has two or more monitor ports, there are a few programs that only display on the monitor Windows detects as the Primary monitor (# 1). E.g. Power DVD won't display the video playback of a DVD on the Secondary monitor (# 2) as seen by Windows.